#### Lecture 4 ###
# Michelle Szucs

# To download as a Python file, right-click the link
# and select "Save link as..."

# Comment out code you don't want to run, or put
# assert False
# (uncommented) to stop code execution after that point.

############# import statements ########################

import math

sin90 = math.sin(math.pi/2)
print "sin90:", sin90

# You can also change the name you use to call the module
# by using the "as" keyword.
# You might do this to shorten a module name or make sure
# the module name doesn't duplicate the name of one of your
# variables.

import math as totallyNotMath

sin90 = totallyNotMath.sin(totallyNotMath.pi/2)
print "sin90:", sin90


############# while loops - the right way ####################

isDone = False # Boolean variable - "inital condition"

##def enterNames(name):
##    do stuff - dummy function to pretend we do things

while not isDone: # this loop will run if isDone is False
    newName = raw_input("Please enter a name. ")
    #enterNames(newName) # dummy function call
    done = None # need to create the variable
    # Now we want to force the user to enter a valid input.
    while not (done == "no" or done == "yes"): # https://piazza.com/class#winter2013/6s189/39
        done = raw_input("Would you like to enter more names? Please enter yes or no. ")
    if done == "no":
        # The next time the while statement is checked,
        # not isDone evaluates to False, and the loop
        # doesn't run again.
        isDone = True

########### while loops - the less right way ##############
        
# You *can* use while loops in this manner, but it's better
# to use a for loop.

i = 0
while i < 10:
    print "Bad while loop:", i
    i+=1 # i = i+1

################ Composite operators ######################

# See tutor problem Wk 2.1.3: Composite Operators
# Composite operators make variable assignemnts.
# i += 1 is the same as i = i + 1.
# That means that the left-hand side of the equation needs
# to be a variable name.

##################### for loops ########################### 

# Using range - equivalent to previous while loop
# The variable i - which is  automatically created when we
# use it in the for loop - takes on the values 0, 1, 2, 3,
# 4, 5, 6, 7, 8, and 9
for i in range(10): # for i in range(0, 10, 1)
    print "for loop 1:", i

# Iterating over a string
name = "Michelle"

# letter takes on the values "M", "i", "c", etc.
for letter in name:
    print "for loop 2:", letter

# Another to do the same thing
for letter in "Michelle":
    print "for loop 3:", letter

# Iterating over a string with a while loop - uncomment to run
##i = 0
##while i < 8:
##    print name[i]
##    i += 1
    
# Iterating over a tuple
for letter in ("M","i","c","h","e","l","l","e"):
    print "for loop 4:", letter